Even though Colorado will permit the legal possession and use of marijuana starting Wednesday, employers may also legally fire workers who test positive for the drug.

Amendment 64, the ballot initiative passed by voters in November 2012 that essentially legalizes marijuana, permits employers to prohibit its use both on and off the job.

Pot proponents said that’s an unfair double standard.

“No business would ever fire an employee simply because they had a couple beers over the weekend or a cocktail after work,” said marijuana advocate Mason Tvert. “So there’s really no logical reason why an employee should be fired just for using marijuana over the weekend — which is a far less harmful substance.”

But Tvert admits there is legal justification for the discrepancy.

“It’s currently still illegal under federal law to use marijuana and until that changes, they’re going to have that right,” said Tvert.

Employers also have legal precedent on their side.

A Colorado appeals court upheld the 2010 firing by Dish Network of a man who legally smoked medical marijuana while off duty. That case is now being heard by the Colorado Supreme Court.

Because random drug tests can’t determine exactly when marijuana was consumed, and the drug can remain in the human body for 30 days or more, off-duty pot use can put workers in jeopardy.

“I do think that will soon change,” said Tvert. “I think private businesses are already becoming less and less interested in drug testing for marijuana. They don’t want to fire qualified employees, and have to recruit, and rehire and retrain.”